A convection heat loss suppressing solar collector is described in the Jeffrey M. Cohen et al. U.S. Pat. Nos. 4,022,188 and 4,132,219. According to the Cohen et al. U.S. Patents, a generally planar horizontally extended absorber is provided in a downwardly directed insulating outer shell or housing. A radiation accepting aperture is formed in the lower surface of the insulating absorber housing and is covered with a solar energy transmitting sheet. A reflecting element is disposed beneath the insulating absorber housing for directing radiant solar energy upwardly through the aperture onto the absorber. A heat transfer fluid circulates in a duct through the absorber for transfer and storage of heat energy.
The solar collector apparatus of Cohen et al. is a "non-steered reflector", incapable of tracking the sun. As a result, the absorber of Cohen et al. is of extended planar configuration over an aperture of extended width in an endeavor to collect solar energy reflected at different angles from the reflector surface corresponding to different angles of elevation of the sun for specified solar collecting hours. The elongate reflecting surface is a section of a cylindrical parabola with the vertex of the parabola at one end of the reflecting surface. The width of the aperture extends along the axis of the parabola the preselected width distance for accepting the desired range of reflecting angles corresponding to different elevations of the sun.
A disadvantage of the Cohen et al. solar collector is that the extended planar absorber and wide absorber box shade and deflect a substantial portion of solar radiation from the reflector surface. The extended width of the aperture also increases the uninsulated area of the absorber housing with consequent increase in conduction heat loss. Furthermore, without elevational tracking, the Cohen et al. solar collector cannot provide optimum concentration and focusing of solar radiation at the different reflecting angles corresponding to different elevations of the sun. The extended planar absorber and wide absorber box are therefore required to pick up the unfocused solar radiant energy over a wide focal band rather than a concentrated focal line.
Because of the absence of azimuthal tracking around the horizon, the Cohen et al. solar collector loses substantial solar radiant energy by side reflections missing the absorber as the sun moves to azimuthal angles on either side of the reflector surface. If the length of the Cohen et al. planar absorber and insulating housing are increased to capture more of the side reflections, there is greater material cost and increased surface area and conduction heat loss. Without elevational and azimuthal tracking the Cohen et al. solar collector is limited overall to only several hours of efficient practicable solar energy collection during the day.